Generally, a hydraulic excavator as a construction machines, is largely constituted by an automotive vehicular lower structure, an upper revolving structure which is swingably mounted on the vehicular lower structure, and a working mechanism liftably mounted at the front side of the upper revolving structure.
Further, the upper revolving structure is largely constituted by a revolving frame which is arranged to serve as a support structure, an engine for driving a hydraulic pump which is mounted on a rear portion of the revolving frame, and a cab which is built on the front side of the engine. That cab is composed of a floor member having a floor panel laid on a front portion of the revolving frame, a seat support platform which is mounted on the floor panel of the floor member, an operator's seat which is mounted on the seat support platform, and a cab box which is provided on the floor panel and arranged to enclose four sides and top side of the operator's seat.
Furthermore, for the purpose of improving the working environment of a dwelling space within a cab for operators, an air conditioner unit is installed to condition inhaled air to supply conditioned cool or warm air. The air conditioner unit of this sort is installed, for example, in an air conditioner unit accommodation room which is provided between the seat support platform and the floor panel (e.g., for example, Patent Literature 1: Japanese Patent Laid-Open No. 2002-121770).
In some cases, the operation of an air conditioner unit on a hydraulic excavator is switchable between an internal air circulation mode, in which internal air within a cab is inhaled and conditioned for supply to the cab, and an external air induction mode in which external air is taken in from outside the cab through a duct to supply conditioned air to the cab. In such a case, for example, an external air inlet which takes in external air is opened in an outer peripheral surface of the revolving frame to avoid inflow of warmed air from the side of the engine. The external air inlet, which is provided on the revolving frame side, is connected to an air conditioner unit within the cab by the use of an air intake hose which is provided separately (e.g., for example, Patent Literature 2: Japanese Patent Laid-Open No. H4-27618).
Now, in the case of the hydraulic excavator in Patent Literature 2 mentioned above, the external air inlet is opened in an outer peripheral surface of the revolving frame to avoid inflow of warmed air from the side of the engine, and the external air inlet and the air conditioner unit is connected by a hose which is provided separately. This hose has a wide passage area in section to ensure passage of air, and requires an additional hose installation space under a floor assembly.
However, in the case of a small hydraulic excavator like the one as described in Patent Literature 1, which is generally called “a mini shovel”, the upper revolving structure is built in a compact form, for example, with a swing motor, control valve and a large number of hydraulic hoses are compactly laid out in a narrow space under the floor panel of the cab.
Accordingly, in the case of a small hydraulic excavator as mentioned above, a difficulty is encountered in finding an extra space for installation of a hose which connects an external air inlet with an air intake port of an air conditioner unit. Therefore, an external air inlet has to be necessarily located at a position which is not distant enough from an engine, despite degradations in cooling efficiency caused by inflow of heated air from the engine.